1. Field of the Invention
The present invention relates to an ink set, particularly to an ink set suitable for an ink-jet system. The present invention also relates to an image-forming method employing the ink set. The present invention further relates to an ink-jet apparatus employing the ink set.
2. Related Background Art
Ink-jet recording is a recording method which conducts recording by ejecting ink droplets onto a recording medium such as a paper sheet. In particular, the ink-jet recording method disclosed in JP-B-61-59911, JP-B-61-59912, and JP-B-61-59914 ("JP-B" herein means examined Japanese patent publication) employs an electro-thermal transducer which supplies energy to the ink to form bubbles in the ink to eject ink droplets. This method enables construction of a multiple orifice recording head having orifices arranged at a high density, thereby giving high-quality images with high resolution at a high recording speed.
In conventional ink-jet recording, the ink contains water as the main component, and additionally a water-soluble high-boiling solvent as a minor component for prevention of drying of the ink and clogging of orifices. In recording on plain paper with such an ink, fixation of the ink is likely to be insufficient and the formed image tends to be irregular, probably due to non-uniform distribution of the filler or the sizing agent in the recording paper. In particular, in color image recording, a plurality of color ink droplets are successively projected in superposition before the respective inks are sufficiently fixed on the paper sheet, thereby causing running of the ink or irregular mixing of the colors at the color border portions (this phenomenon is called "bleeding") and as a result, satisfactory images cannot be obtained.
For improvement of ink fixation, JP-A-55-65269 ("JP-A" herein means unexamined Japanese patent laid-open application) discloses addition of a compound for enhancing penetration such as a surfactant to the ink, and JP-A-55-66976 discloses an ink mainly composed of a volatile solvent. The former method improves the ink fixability and decreases the bleeding of the ink to a certain degree due to the promotion of penetration of the ink into the recording paper sheet, but involves disadvantages such that the coloring matter penetrates excessively deep together with the ink into the recording paper sheet to result in low density and low saturation of the image, and the ink runs laterally to result in less sharpness of the edge of the image and less resolution. On the other hand, the latter method tends to cause clogging of the orifices of the recording head by evaporation of the solvent, in addition to the aforementioned disadvantages of the former method.
For solving the above problems, methods are disclosed in which a liquid for ameliorating the image quality is applied onto the recording medium prior to the application of a recording ink. For example, JP-A-63-299971 discloses a recording method in which a liquid containing an organic compound having two or more cationic groups in the molecule is applied onto the recording medium and thereafter recording is conducted with an ink containing an anionic dye. JP-A-64-9279 discloses a recording method in which an acidic liquid containing succinic acid or the like is applied on the recording medium and then recording is conducted with an ink containing an anionic dye. JP-A-64-63185 discloses a recording method in which a liquid capable of insolubilizing the dye is applied before recording with the ink.
The above methods intend to deposit the dye itself for prevention of bleeding and for improvement of the water resistance of the image. However, the insolubilization of the dye remarkably depresses its coloring property due to agglomeration of the dye.
In particular, a black ink containing a water-soluble black dye, when used for such an image formation, causes agglomeration of the dye, which noticeably decreases the coloring ability and tinges the black portion of the image with red, which is known as the bronzing phenomenon, to impair the quality of the recorded image.